This invention is pertinent to a navigation system and relates in particular to a navigation system, a route searching method, and a map information guide method for appropriately bypassing a time restriction road and searching for a route from the current position of the vehicle to a destination and guiding the driver through the route.
In recent years, a navigation system for displaying the current position of a mobile unit on a map and searching for an optimum route to a destination and guiding the user through the route is developed heavily. Recently, an attempt is made to provide a navigation system for guiding the user through a bypass avoiding traffic restriction and congestion based on road traffic information, etc., thereby enabling the user to drive to the destination more smoothly.
In route searching in such a navigation system, if candidates for a route found as the user sets a destination contain a time restriction road, hitherto, route searching is conducted assuming that the road is permanently passable or impassable. Thus, the navigation system guides the user through a route taking a long way to avoid an essentially passable road or guides the user through an essentially impassable road and when the mobile unit is about to reach a time restriction road, the user cannot advance the mobile unit because of the time restriction, etc.; this is a problem.
Although a run route to bypass a time restriction road is displayed, the user cannot understand why the route presented on the display screen indicates a bypass taking a long way; this is a problem.
Further, if the user makes a determination as to which route to select and drives while seeing a map displayed on the display screen without setting a route, although time restriction information exists, it is not displayed on the display screen and thus the user drives while being unaware of a time restriction road and suddenly encounters the time restriction road, and his or her way is blocked; this is a problem.
Recently, however, various navigation systems and route searching methods for considering the restriction time period of such a time restriction road to search for an optimum route and guide the user through the optimum route or differentially display a time restriction road and guide the user are proposed.
For example, the Unexamined Japanese Patent Application Publication No. Hei11-304514 discloses a method of estimating a passage schedule time through a road where a traffic restriction time period is set and determining whether or not the road can be used, thereby searching for a recommended route without excluding time restriction roads. A route searching apparatus using this method performs searching consisting of initial searching and re-searching. In the initial searching, the route searching apparatus searches for a recommended route by assuming that there is no restriction as to a link outside the range of a predetermined distance range, such as 10 km, in the periphery of the current position. In the re-searching, the route searching apparatus checks to see if a time restriction link exists in a predetermined range in the destination direction on the recommended route each time the user drives a predetermined distance, for example. If a time restriction link exists, the route searching apparatus estimates the vehicle passage time through the link and checks to see if the estimated time is within the range of the restriction time period including predetermined times preceding and following the restriction time period. If the time is within the range, the route searching apparatus re-searches for a route so as to bypass the link and updates the recommended route data and display of the recommended route.
The Unexamined Japanese Patent Application Publication No. Hei11-287667 discloses a method of making it possible to also set an appropriate route and guide the user considering the passage restriction on a season passage restriction road. A vehicle-installed navigation system using the method calculates the entry prediction time into a dynamic restriction link on a route every given time and if the situation is changed to a situation in which entry into the dynamic restriction link is not allowed at the calculated entry prediction time, a route re-calculation request is made. If the current position is near to a bypass-possible intersection, if a dynamic restriction link exists in a given range, or if the vehicle goes off the shortest route, a route re-calculation request is also made. Therefore, even if the arrival prediction time at a dynamic restriction link varies depending on the vehicle run state and the presence or absence of restriction changes after a route is once set, an optimum route, namely, an appropriate route bypassing the dynamic restriction link or the shortest route containing the dynamic restriction link can be again set.
The Unexamined Japanese Patent Application Publication No. Hei9-222332 discloses a method of searching for an optimum route also including a restriction road and aggressively using the restriction road if the restriction road is passable. A vehicle route guide apparatus using the method searches for an optimum route from the current place where the vehicle exists to the destination also including passage restriction road zones. If the found optimum route contains a passage restriction zone, the vehicle route guide apparatus determines whether or not passage is allowed a predetermined distance before the passage restriction zone. If passage is not allowed, the vehicle route guide apparatus excludes the passage restriction zone and again searches for an optimum route from the beginning. Then, the vehicle route guide apparatus displays the optimum route and the current place where the vehicle exists on a road map, and guides the user to the destination.
The Unexamined Japanese Patent Application Publication No. 2001-159534 discloses a method of superposing the current position of the vehicle on a map for display and determining whether or not partial restriction information exists in the target road and if partial restriction information exists, displaying the road in a different display mode from the normal display mode, thereby making it possible to report precise road information to the user. To draw in a map drawing section, a navigation system using the method determines whether or not the road zone to be drawn has partial restriction information of time period traffic suspension, etc., from restriction information data read from data read memory. If the road zone has partial restriction information, the road zone is drawn in a preset color different from the normal road zone drawing color. If the road zone does not have partial restriction information, the road zone is drawn in the normal road zone drawing color. This enables the user to previously recognize that partial restriction information exists in the forward road by seeing a display section at driving time, and enables the user to determine a route with lead time.
However, in the navigation system as described above, the range to check to see if a time restriction road exists is fixed regardless of whether the area of the current position of the vehicle is an urban or suburban area. Thus, a search must be made for a time restriction road over a wide range more than necessary in an urban area, etc., where a large number of complicated restrictions are placed or arrival prediction times at a large number of time restriction roads are all calculated and thus processing of determining the presence or absence of restriction on each time restriction road becomes very complicated and it takes time more than necessary in searching for a route bypassing the time restriction roads; this is a problem.
In differential display of a time restriction road, the presence of the time restriction road can be recognized, but the time restriction road is not displayed in such a manner that the relationship between the restriction time period and the current time can be recognized and therefore there is a problem of taking the trouble to take a long way to bypass the passable road at the current point in time.